Induction furnace



April 11, 1950 R. L. LINDNER ET AL INDUCTION FURNACE Filed Sept. 30, 1948 fizz 212147.? 31129 1. [Wm/1? Patented Apr. 11, 1950 INDUCTION FURNACE Ralph L. Lindner, Cleveland, and Tyler K. Hayes,

Cleveland Heights, Ohio, assignors to Thompson Products, Inc.,- Cleveland, Ohio, at corporation of Ohio Application September 30, 1948, Serial No. 51,922

2 Claims. (Cl. 13-29) This invention relates to an induction furnace and more particularly deals with a bailled hearth construction for a molten metal holding furnace which minimizes sla or oxide inclusions in the metal.

This invention further includes a method of preserving easily oxidized metals in pure molten form for castings which are relatively free from slag inclusions or so-called "hard spots.

The invention will hereinafter be specifically described in connection with the melting of aluminum and the holding of molten aluminum in a stable condition for casting because this metal is commonly melted in electric induction furnaces and is easily spoiled by slag inclusions. However, it will be understood that the bailied hearth construction of this invention will minimize slag inclusions in any metal melted in the furnace. Aluminum slag and aluminum metal have about the same specific gravity so that the slag does not float oil out of the body of molten metal.

A conventional induction furnace generates power within the metal and relatively low temperatures prevail in the hearth above the molten metal. These furnaces are usually provided with a deep bath of substantially small cross-section and can maintain any desired temperature in the bath. Although temperatures throughout a typical bath are usually quite uniform, it is not unusual that slag formations appear in the molten metal due to oxidation of the aluminum. The rate of oxidation and slag formation is materially increased when the metal bubbles freely in the bath and as explained above, the slag will not rise to the surface of the molten metal but remains trapped in the body of the metal.

Heretofore slag inclusions in aluminum castings have been a constant source of trouble and expense inasmuch as these inclusions provide hard spots which have caused breakage of tools during machine finishing operations and have resulted in spoiling of a relatively high number of casting units.

An induction furnace constructed in accordance with our invention provides for the partitioning of the furnace hearth into two distinct compartments, thereby confining agitation of the molten metal to one side of the hearth without sacrificing the heat transfer characteristics of the furnace. This, therefore, constitutes one object of our invention.

Another object of our invention is to provide an induction furnace of the so-called holding type, whereby relatively slag free molten alumi- 2 num may be drawn for the purpose of pouring castings.

Another object of our invention is to provide an improved method of melting metal and producing castings relatively free of objectionable slag inclusions.

A further object of our invention is to provide an improved induction furnace for meltin metal and maintaining metal in a molten state.

The novel features and characteristics of our invention are set forth in particularity in the appended claims. Our invention, itself, however, both to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following detailed description and the accompanying drawings, in which Figure 1 is a vertical sectional view of an induction furnace embodying our invention;

Figure 2 is a cross-sectional view taken on line 11-11 of Figure 1, and

Figure 3 is a view similar to Figure 2, but showing an alternative embodiment of our invention.

On the drawings:

Referring to Figures 1 and 2, an induction furnace suitable for aluminum metal and the like is indicated generally at It as comprisin a furnace secondary H and crucible l2.

The furnace secondary ll may be constructed in accordance with any form well known in the art and is herein shown as compiising a well-like structure packed with refractory material to define three vertical channels [3, l4 and [5 connected at the bottom by a straight horizontal chamber it of larger cross-section. The channels open upwardly into a furnace secondary outlet channel or sump Ila extending across the furnace near one side thereof.

The two loops formed by the center channel I in connection with each of the outside channels l3 and I5 and with the corresponding part of the chamber Ii are interlaced with a pair of primary coils indicated at I! wound around closed cores of laminated steel indicated at I8. The coils H are connected to a suitable source of electric current.

The crucible l 2, formed in a conventional cubical shape, is packed with refractory material to define a bath or hearth I! located at the top of the sump Ha and ehannefs l8, I4 and II.

A baflle partition 20 is inserted into the hearth is adjacent to and parallel with the outlet channel or sump Ila thereby effectively partitioning the hearth it into two compartments designated on the drawings as lie and lib. The partition 3 .llis .preferahlymarle or amaterial having high heat conductivity properties such as silicon car- A perforated partition, as shown in Figures 1 D and 2 allows the agitated bubbling metal emanating from the outlet channel Ha to be confined in compartment I9a and permits the molten metal in compartment 19b to remain quiet. All

metal for casting is then ladled and poured irom the quiet side 1912 of the pot i9. Charges and ladle dregs are placed in compartment 89a.

The openings 21 permit greater heat conductivityfrom one side of the hearth to the other and also permit the molten metal to flow. from the compartment lSa into the compartment 1912. However, in accordance with Newton's law of gravitation any slag particles formed in the agitated metal contained in compartment l9a will not flow through the holes 2! due to the presence and gravitational influence of the bafiie partition 23. Thus, slag particles will be attracted towards the partition 20 away from the openings 21in the partition and will ultimately fiOw to the sides of the compartment. This is, of course,

highly desirable since the molten metal in the compartment [9b is kept relatively free of bothersome slag formations and castings may then be produced free of slag inclusions.

A solid hearth partition, as shown in Figure 3, accomplishes a complete physical isolation of the agitated molten metal emanating from the secondary H from the metal contained in the quiet Y side 19b, yet the partition 20 passes a sufficient quantity of heat to keep the molten metal at a suitable temperature for pouring. Metal for casting, therefore, may be ladled and poured from the compartment 191) and the supply may be renewed with a fresh charge of molten metal from time to time as may be necessary.

It will be apparent to those skilled in the art that we have described an improved induction furnace which not only raises and maintains molten metal at correct pouring temperatures, but facilitates the production of improved castings relatively free of slag inclusions.

While we have shown a particular embodiment of our invention,-it will, of course, be understood that we do not wish to be limited thereto since modifications of-certain details may be made without departing from the spirit of our inven-, tion. We desire to be limited, therefore, only by the scope of the appended claims and the prior art.

We claim as our invention:

1. In an induction furnace having a furnace secondary sump for heating molten metal by electromagnetic induction and having a crucible above said sump, said crucible having an upright partition wall of high thermal conductivity extending across the crucible in continuous contact with the side walls and bottom thereof, and

dividing the crucible, said crucible having separate compartments on opposite sides of said partition, one of said compartments being separated from said sump, the other of said compartments being above said sump, said partition having an opening therein of small cross-sectional area relative to the upright wall area 0! the partition and lying substantially below the top of and substantially above the bottom of the partition, and said opening being sufiiciently large to accommodate low velocity flow from the compartment above the sump to the compartment separated from the sump whereby molten metal can flow through the opening but slag inclusions will tend to remain in the compartment above the sump.

2. In an induction furnace having a furnace secondary sump for heating molten metal by electromagnetic induction and having a crucible above said sump, said crucible having an upright partition wall of high thermal conductivity ex= tending across the crucible in continuous contact with the side walls and bottom thereof, and dividing the crucible, said crucible having separate compartments on opposite sides of said partition, one of said compartments being separated from said sump, the other of said compartments being above said sump, said partition having a plurality of triangular shaped openings therein, each of said triangular shaped openings having a small cross-sectional area relative to the upright wall area of the partition and lying substantially below the top and substantially above the bottom of the partition, said triangular shaped openings being suf iciently large to accommodate low velocity flow from the compartment above the'sump to the compartment separated from the sump whereby molten metal can flow through the triangular shaped openings but slag inclusions will tend to remain in the compartment above the sump.

' RALPH L. LINDNER.

TYLER K. HAYES.

REFERENCES CE'EED The following references are of record in tie file of-this patent:

UNITED STATES PATENTS Number Name Date 859,134 Snyder July 2, 1907 859,137 Snyder July 2, 1907 1,061,433 Wicker May 13, 1913 1,226,651 Fort May 22, 1917 1,737,566 Brown Dec. 3, 1929 1,768,881 Brace Julyl, 1930 1,878,532 Northrup Sept. 20, 1932 2,195,071 Bahney et a1. Mar. 26, 1949 2,250,155 Ferguson July 22, 1941 2,368,173 Tama et a1. Jan. 30, 1945 FOREIGN PATENTS Number Country Date 3,291 Great Britain Feb. 7, 1914 France Jan. 11, 194 3 OTHER REFERENCES Wilcox: Electric Heating, 1st edition, 1928, Me- Graw-Hill Book Company, Inc. 

